1. Field of the Invention
The invention pertains to a method for determining a power by means of which mechanical energy is exchanged between a stationary machine and a shaft assembly which traverses the machine along a given axis and which rotates about the axis with a given angular velocity, and whereby the energy in the shaft assembly flows along the axis.
The invention further pertains to the determination of a power which is output by a machine onto a shaft assembly, and to the determination of a power which a machine absorbs from a shaft assembly.
2. Description of the Related Art
Several kinds of methods and devices for determining a power with which mechanical energy is exchanged between a stationary machine and a rotating shaft assembly have become known in the pertinent art. In particular, there has become known a device in which the determination of the power is derived from a torque which becomes active in a test specimen introduced into the shaft assembly and which causes torsion in the latter. The test specimen may, for example, be an appropriately tapered piece of the shaft assembly which is provided with suitable sensors.
With regard to specific prior art publications, reference may be had to U.S. Pat. Nos. 5,440,938 and 5,452,616 (corresp. EP 0 609 726 A2), GB 2 262 345 A, U.S. Pat. No. 5,215,145 (corresp. EP 0 412 780 A2), and to an extract from "Patent Abstracts of Japan", Volume 11, No. 35 (P542) [2482]. Each of these documents relates to a measurement method and a measuring device for determining a power with which mechanical energy flows through a rotating shaft. The device respectively comprises a plurality of shaft marks provided on the shaft, a plurality of stationary sensors each assigned to a shaft mark, and means for evaluating signals which are output by the sensors and from which the power is calculated. In each case, the shaft between the shaft marks is configured simply and without structure, that is to say it is a slight spacing from one another. This configuration permits the torsion of the shaft occurring for the given power to be predicted theoretically and renders it possible for the power to be measured directly and in absolute terms using such predictions. While these systems provide certain advantages, the devices are deprived of flexibility with regard to further developments. Also, every known device and every known method must manage with a comparatively slight torsion of the rotating shaft, which may lead to substantial impairment of the accuracy of the measurement.
This invention is particularly directed to monitoring a machine set consisting of a plurality of machines, with the machines of the machine set being arranged successively along a common, rotating shaft assembly. For example, the inventor gave particular consideration to a single-shaft turbo set comprising, as a rule, a plurality of steam turbines, in some instances a gas turbine, and a generator. With regard to this application, reference may be had once again to U.S. Pat. Nos. 5,440,938 and 5,452,616 (EP 0 609 726 A2). It is often most important in such an environment to ensure carefully tune and balance the supply and extraction of mechanical energy to the individual machines, in order to load the machines evenly and to avoid overloading. Overloading can consist in this case both in an excessive load and in unplanned idling; the last criterion applies, in particular, to a steam turbine which given inadequate application of steam operates no longer as a turbine but as a compressor and can thereby be exposed to extreme temperature loads.